Conventional Programmable Power Switching Systems (PPSS) and Programmable Power Switching Elements (PPSE) and methods are used for both AC and DC current applications. Such systems are variously known as “smart power switches,” “protection systems,” “electronic fuses,” etc. Most of the systems currently known in the art are directed to detection of short circuits or open loads and to the subsequent execution of steps to protect and isolate the energy source and the load branch. These systems fail to provide any protection or redundancy within the relevant switch if the MOSFET malfunctions, however. Moreover, if there is a delay between the detection of the short circuit and the disconnection of the load branch from the energy source, the MOSFET, the shorted load, and the power source are exposed to the overcurrent, which may reduce the entire system voltage or even melt the MOSFET.
The systems currently on the market mainly comprise mechanical, thermal, and magnetic fuses. More recently, electronic fuses based on MOSFETs, SiC MOSFETs, IGBTs, power transistors, and SCR/Triac have been developed. These conventional systems can detect a short circuit and then disconnect the load from the voltage source, but until the disconnection has been completed, the voltage source and the MOSFET(s) absorb a high current. The relatively high internal resistance of batteries and fuel cells puts constraints on the system reliability, however, because these types of fuses cannot act quickly enough to prevent the battery from experiencing a high current surge from which the fuses are damaged.
For example, if the energy source is a 24 V battery with an internal resistance of 0.5Ω, a short circuit of 50 A for 1 mSec causes a short to the battery, causing some or all loads in the electric switching system to lose energy. Due to the high short circuit current, connecting capacitors near the battery does not provide a practical solution to the problem.
Similarly, if the energy source is, for example, a 24 V vehicle battery with an internal resistance of 1 mΩ connected to a MOSFET having an internal resistance of 5 mΩ, a short circuit conducts a current of 24 V/0.006Ω=4000 A. Thus, a delay prior to detection of the short circuit of 1 ms causes a short to the battery, causing some or all loads in the electric switching system to lose energy. Due to the high short circuit current, the MOSFET is melted.
In cases in which the power source has a high impedance, power switching systems known in the art generally introduce significant undesired surge current into the circuit. On the other hand, in cases in which the power source is a very low impedance battery or power supply, a short circuit produces a high current, at least transiently. A typical circuit that includes a MOSFET cannot handle such a transient high current (on the order of thousands of amperes) even for 1 μs. Such an event melts the transistor and permanently shorts the load.
Therefore, there is a need in the art for a PPSS/PPSE that overcomes some or all of the deficiencies of the prior art.